U.S. patent number 7,519,033 [Application Number 10/556,001] was granted by the patent office on 2009-04-14 for system and method for measurement report time stamping to ensure reference time correctness.
This patent grant is currently assigned to Koninklijke Philips Electronics N.V.. Invention is credited to Amjad Soomro.
United States Patent |
7,519,033 |
Soomro |
April 14, 2009 |
System and method for measurement report time stamping to ensure
reference time correctness
Abstract
A system and method is provided that resolves a possible
ambiguity in WLAN measurement reports by having a measuring entity
include timer values in returned measurement reports. The time a
measurement was requested to be performed and the actual time it
was done by a measuring entity can be compared by the receiver to
ensure that no ambiguities occurred.
Inventors: |
Soomro; Amjad (Hopewell
Junction, NY) |
Assignee: |
Koninklijke Philips Electronics
N.V. (Eindhoven, NL)
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Family
ID: |
33436763 |
Appl.
No.: |
10/556,001 |
Filed: |
May 3, 2004 |
PCT
Filed: |
May 03, 2004 |
PCT No.: |
PCT/IB2004/001466 |
371(c)(1),(2),(4) Date: |
November 08, 2005 |
PCT
Pub. No.: |
WO2004/100450 |
PCT
Pub. Date: |
November 18, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070002806 A1 |
Jan 4, 2007 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60469194 |
May 9, 2003 |
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60503849 |
Sep 17, 2003 |
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Current U.S.
Class: |
370/338; 370/345;
455/423; 455/524; 455/67.11; 455/502; 370/350; 370/332 |
Current CPC
Class: |
H04L
43/067 (20130101); H04L 43/106 (20130101); H04W
24/10 (20130101); H04W 84/18 (20130101); H04W
84/12 (20130101) |
Current International
Class: |
H04L
12/26 (20060101) |
Field of
Search: |
;370/310,328,277-278,332,345-350
;455/67.11,67.14,115.1,524,502,507,41.2,423 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
"Transmitter Power control (TPC) and Dynamic Frequency Selection
(DFS) Joint Proposal for 802.11h WLAN", by S. Choi et al, May 2001.
cited by other .
"Proposed Text for Radio Measurement Requests and Reports", by
Daryl Kaiser, Mar. 13, 2003. cited by other .
Amendment 5: Spectrum and Transmit Power Management Extensions in
the 5 GHz band in Europe, XP 002292634, (Noted the Date is: Oct.
14, 2003). cited by other.
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Primary Examiner: Afshar; Kamran
Attorney, Agent or Firm: Liberchuk; Larry
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application claims the benefit of U.S. provisional application
Ser. No. 60/469,194 filed May 9, 2003 and U.S. provisional
application Ser. No. 60/503,849 filed Sep. 17, 2003, both of which
are incorporated herein in whole by reference.
Claims
The invention claimed is:
1. A method for creating a measurement report among a plurality of
stations in a wireless local area network (WLAN), comprising the
steps of: receiving by a measurement capable station of said
plurality of stations a measurement request for at least one
measurement report element to be made at a given time; recording by
the measurement capable station said at least one measurement
report element; creating by the measurement capable station a
measurement report comprising said at least one measurement report
element as one of measurement report elements contained therein;
respectively time-stamping with an absolute time reference at least
one of said at least one recorded measurement report element and
said measurement report; and transmitting by the measurement
capable station said created measurement report.
2. The method of claim 1, wherein said time-stamping step further
comprises the step of setting by the measurement capable station
each said absolute time reference to a time synchronization
function (TSF) timer value.
3. The method of claim 1, further comprising the steps of: if at
least one measurement element has been time-stamped with an
absolute time reference, determining by the measurement capable
station an earliest said absolute time reference of a measurement
report element, and setting by the measurement capable station said
measurement report time-stamp to said determined earliest absolute
time reference of a measurement report element.
4. The method of claim 3, wherein said time-stamping step further
comprises the step of setting by the measurement capable station
each said absolute time to a time synchronization function (TSF)
timer value (306).
5. A method for creating an autonomous measurement report having at
least one measurement report element, among a plurality of stations
in a wireless local area network, comprising the steps of:
recording by a measurement capable station of said plurality of
stations at least one pre-determined measurement report element;
optionally time-stamping with an absolute time reference by the
measurement capable station said at least one recorded measurement
report element; creating by the measurement capable station an
autonomous measurement report comprising said at least one
measurement report element; optionally time-stamping with an
absolute time reference of the earliest time of a measurement
report element contained therein said autonomous measurement
report, and transmitting by the measurement capable station said
autonomous measurement report, wherein, at least one of said
autonomous measurement report time-stamp and said at least one
measurement report element time-stamp is included in said
autonomous measurement report.
6. The method of claim 5, wherein each said time-stamping step
further comprises the step of setting by the measurement capable
station said absolute time-stamp to a time synchronization function
(TSF) timer value.
7. A method for ensuring correctness of a time reference of a
requested measurement among a plurality of stations (STAs) in a
wireless local area network (WLAN), comprising the steps of:
transmitting by a first station a request for at least one
time-stamped measurement report element to be performed at a given
time; receiving by a second station both the measurement request
and a corresponding measurement report comprising the requested at
least one measurement report element and at least one time-stamp
comprising an absolute time reference of when the measurement
recorded therein was done; comparing by the second station the
given time of the measurement request with the at least one
time-stamp to determine correctness of the time-stamp.
8. The method of claim 7, wherein said receiving step further
comprises the step of receiving a measurement report having each
said Time Stamp set using a time synchronization function (TSF)
timer value.
9. An apparatus configured for resource measurement among a
plurality of stations in a wireless local area network (WLAN),
comprising: a receiver for receiving an incoming signal; a
measurement acquisition circuit that measures resources of said
incoming signal received therein as at least one measurement report
element; a timer that provides an absolute time reference; a
control processor, coupled to said measurement acquisition circuit
and said timer and beginning at a predetermined absolute time,
configured to acquire at least one measurement report element of
said incoming signal and optionally associate one of (1) an
absolute time reference of the start of the first measurement
reported within a measurement report as a time-stamp and (2) an
absolute time reference of the start of each measurement report
element reported therein with a measurement report element
time-stamp.
10. The apparatus of claim 9, further comprising: a memory, coupled
to said control processor to store said obtained measurement report
elements and optionally said associated measurement report element
time-stamps; and wherein, said control processor is further
configured to compare the predetermined absolute time with at least
one said absolute time-stamp to determine correctness of said at
least one absolute time-stamp.
11. The apparatus of claim 9, further comprising a receiver for
receiving a measurement request comprising at least one measurement
request element to be measured and reported as a measurement report
element and the predetermined time to staff measuring.
12. The apparatus of claim 11, wherein said measurement request is
transmitted by a station of said plurality of stations.
13. The apparatus of claim 11, wherein said measurement request is
transmitted by an access point of said plurality of stations.
Description
The present invention relates to Local Area Network communication,
and more particularly to a system and method for time stamping a
measurement report that ensures correctness of a reference
time.
In general, there are two variants of WLANs: infrastructure-based
and ad hoc-type. In the former network, communication typically
takes place only between the wireless nodes, called stations (STA),
and an access point (AP) that is also a STA., which together form a
basic service set (BSS). Communication takes place directly between
wireless nodes (STAs) which form an independent basic service set
(IBSS) in the ad hoc-type network.
In a WLAN, measurements are requested and reported between Radio
Measurement-capable STAs. Measurements on non-serving channels are
dedicated measurements, requiring the measuring STA to interrupt
its normal operation, switch channels and acquire radio
measurements. Measurements on a serving channel are executed by a
STA as concurrent measurements. While a Measurement-capable STA is
responsible for decoding and interpreting each Measurement Report
Frame and assessing its impact on its own performance, the
execution of some Measurement requests is optional and may be
ignored by a receiving STA if its execution would significantly
degrade the STA's performance.
A STA may measure one or more channels itself or a STA may request
other STAs in the same BSS or IBSS to measure one or more channels
on its behalf. When requesting other STAs to measure one or more
channels, a STA employs a Measurement Request Frame specifying
therein at least one Measurement Request element.
The Institute of Electrical and Electronics Engineers (IEEE)
802.11-1999 standard is a protocol standard for wireless LANs
(WLANs) that focuses on the media access control (MAC) and physical
(PHY) layers and is hereby incorporated by reference as if fully
set forth herein. In the IEEE 802.11(h) and IEEE 802.11(k) draft
supplements to this standard, which are hereby incorporated by
reference as if fully set forth herein, measurement requests
include a time reference specifying when a requested measurement is
to be started. For example, as illustrated in FIG. 1A, a
Measurement Offset parameter 100 and an Activation Delay parameter
101 together specify the reference time in IEEE TGh and TGk.
Activation Delay is the measurement activation delay in number of
target beacon transmission times (TBTTs) and Measurement Offset is
the measurement offset in timer units (TUs). FIG. 1B illustrates
the measurement requests allowed.
Due to channel conditions, more than one attempt may be made to
communicate a measurement request to a destination station (STA).
At the receiving STA, if more than one copy of the same measurement
request is received, then the STA discards the most recently
received duplicate packets. This is according to the protocol
specified in the IEEE 802.11 standard.
The discard of duplicate frames at the receiving STA, according to
the IEEE 802.11 protocol, may result in the requesting and
receiving STA each having a different reference beacon from which
each references measurement start times. For example, if a
measurement request is intended to be transmitted in one beacon
period and, due to channel conditions, the recipient STA receives
the frame correctly while its ACK is not received back at the
transmitting STA, and if subsequently the measurement request is
successfully transmitted in another beacon period, then, at the
transmitting and receiving stations the reference beacons
differ.
Embodiments of the present invention provide a method and system
that resolves the ambiguity in a WLAN measurement report by
including timer values in measurement reports. The time a
measurement is requested to be performed and the actual time the
measurement is made can then be compared by the requestor to ensure
that no ambiguity occurs. In an embodiment of the present invention
for an IEEE 802.11 WLAN, time synchronization function (TSF) timer
values are included in measurement reports.
In a preferred embodiment, a Measurement Report Frame and element
are modified to contain a field with an absolute time reference.
For an IEEE 802.11 WLAN the absolute time reference is the value of
TSF time (or part thereof) when requested measurements start. In
all embodiments, comparison is made between the intended
(requested) time to start the measurements and the time
measurements actually started to ensure that no protocol
ambiguities occurred.
FIG. 1A illustrates parameters of a service primitive that requests
the transmission of a measurement request to a peer entity in a
WLAN;
FIG. 1B illustrates the measurement requests allowed in a WLAN;
FIG. 2A is a simplified block diagram illustrating the architecture
of a basic service set (BSS) wireless communication system whereto
embodiments of the present invention are to be applied;
FIG. 2B is a simplified block diagram illustrating the architecture
of an ad hoc-type independent basic service set (IBSS) wireless
communication system whereto embodiments of the present invention
are to be applied;
FIG. 3 illustrates a simplified block diagram of an access point
(AP) and each station (STA) within a particular basic service set
(BSS) or independent basic service set (IBSS) according to an
embodiment of the present invention;
FIG. 4 illustrates a Measurement Report Frame format according to
an embodiment of the present invention;
FIG. 5A illustrates a Measurement Report Element format according
to an embodiment of the present invention; and
FIG. 5B illustrates a Measurement Report mode field of the
Measurement Report Element illustrated in FIG. 5A, according to an
embodiment of the present invention.
In the following description, by way of explanation rather than
limitation, specific details are set forth such as the particular
architecture, interfaces, techniques, etc., in order to provide a
thorough understanding of the present invention. However, it will
be apparent to those skilled in the art that the present invention
may be practiced in other wireless network embodiments that depart
from these specific details.
FIG. 2A is a representative infrastructure basic service set (BSS)
wireless network whereto embodiments of the present invention are
to be applied. As shown in FIG. 2A, an access point (AP) 200 is
coupled to a plurality of mobile stations (STA.sub.i) 201, which,
through wireless links 202 are communicating with each other and
the AP via a plurality of wireless channels. A key principle of the
present invention is to provide a mechanism to time stamp reports
of measurements taken by the STA.sub.i 201 so that protocol
ambiguities can be avoided should they occur and, therefore, makes
it possible to employ corrective actions after the fact. It should
be noted that the network shown in FIG. 2 is small for purposes of
illustration. In practice most networks would include a much larger
number of mobile STA.sub.i 201. FIG. 2B is a representative ad
hoc-type independent basic service set (IBSS) wireless network
whereto embodiments of the present invention are to be applied. As
shown in FIG. 2B, a plurality of mobile stations (STA.sub.i) 201
communicate with each other through wireless links 202 without any
AP.
Referring to FIG. 3, the AP 200 and each STA.sub.i 201 within the
WLAN of FIGS. 2A and B may include a system with an architecture
that is illustrated in the block diagram of FIG. 3. Both the AP 200
and each STA.sub.i 201 may include a receiver 301, a demodulator
302, a measurement circuit 303, a memory 304, a control processor
305, a timer 306, a modulator 307, and a transmitter 308. The
exemplary system 300 of FIG. 3 is for descriptive purposes only.
Although the description may refer to terms commonly used in
describing particular mobile stations, the description and concepts
equally apply to other processing systems, including systems having
architectures dissimilar to that shown in FIG. 3.
In a preferred embodiment, the receiver 301 and the transmitter 308
are coupled to an antenna (not shown) to convert received
measurement reports and transmit desired measurement requests into
corresponding digital data via the demodulator 302 and the
modulator 307, respectively. The measurement acquisition circuit
operates under the control of the processor 305 to the process
received Measurement Report Frames comprising measurements and
corresponding time stamps or to make requested or periodic
measurements (autonomously) in which measurements are conveyed
along with corresponding time stamps in Measurement Report Frames.
FIG. 1B shows possible requestor and measurer combinations for both
IBSS and BSS IEEE 802.11 WLANs embodiments of the present
invention. The timer 306 is used to set the time stamp in the
Measurement Report Frames that indicates the start time of the
measurement being reported.
FIG. 4 illustrates a format for a Measurement Report Frame body 400
according to a preferred embodiment of the present invention. In an
IEEE 802.11 WLAN embodiment of the present invention, the
Measurement Report Frame body 400 uses an Action frame body format
and is transmitted by a STA 201 in response to a Measurement
Request Frame or by a STA 201 autonomously providing measurement
information. In all embodiments, the Category field 401 is set
equal to a value indicating a Radio Measurement category or
Spectrum Management category. The Action field 402 is set equal to
a value indicating a Measurement Report is contained therein. The
Dialog Token field 403 is set equal to a value in a corresponding
Measurement Request Frame. If the Measurement Report Frame 400 is
not being transmitted in response to a Measurement Request Frame
then the Dialog Token field 402 is set equal to zero. In a
preferred embodiment, at least one of (1) the Time Stamp field 404
of a Measurement Report Frame contains the value of an absolute
time reference at the time when the STA started measuring the first
reported measurement and (2) at least one Measurement Report
Element 405 500 is time-stamped 504. The Measurement Report
Elements field 405 contains at least one Measurement Report
Elements 500, as illustrated in FIG. 5A. The number of Measurement
Report elements 500 and length of the Measurement Report Elements
field 405 in a Measurement Report Frame 400 is limited by the
maximum allowed medium access control (MAC) management protocol
data unit (MMPDU) size.
Each Measurement Report Element 500 contains a measurement report
of a measurement made by a STA 201. The format of a Measurement
Report Element 500 of a preferred embodiment is shown in FIG. 5B.
The Element ID field 501 is set to an identifier assigned by a
corresponding measurement request (e.g., according to IEEE 802.11
standard it is 39 for Measurement report.) The Length field 502 is
variable and depends on the length of the Measurement Report field
507. The minimum value of the Length field is 3 (e.g., reporting a
Measurement Mode equal to Incapable or Refused and using a
zero-length Measurement Report field). The Measurement Token field
503 is set equal to the Measurement Token in the corresponding
measurement request. If the Measurement Report element is being
sent autonomously by a STA then the Measurement Token field 503 is
set equal to zero. The Time Stamp field 504 is set to the value of
an absolute timer when the requested measurement is started for
each Measurement Element reported in a Measurement Report Frame
400, which is a TSF timer value for an IEEE 802.11 embodiment of
the present invention. It should be noted that either or both
Time-Stamp fields 404 and 504 can be present in a Measurement
Report.
The inclusion of the actual time 504 of a Measurement Element 500
increases the confidence level of the measurement and when several
STAs 201 report the same measurement at close but different time
actual times 504, this confidence level is further enhanced. In
addition, the frequency of transmitted and requested measurement
reports helps guide STAs 201 in requesting and making measurement
reports, e.g., if a report is received by a STA 201 at 1:00 and
1:05 the STA 201 can request or report measurements at 1:10 to
obtain or provide, respectively, a reliable measurement of a given
element(s).
While the preferred embodiments of the present invention have been
illustrated and described, it will be understood by those skilled
in the art that various changes and modifications may be made, and
equivalents may be substituted for elements thereof without
departing from the true scope of the present invention. In
addition, many modifications may be made to adapt to a particular
situation and the teaching of the present invention without
departing from its central scope. Therefore it is intended that the
present invention not be limited to the particular embodiment
disclosed as the best mode contemplated for carrying out the
present invention, but that the present invention include all
embodiments falling within the scope of the appended claims.
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